Texas Instruments TI-59

The TI-59 was a truly amazing calculator when it was introduced in 1977. A mind-boggling 960 program steps, 100 memories, a magnetic card reader, a rich variety of built-in functions, solid-state program ROM modules, and on top of that, an optional external printer/docking station made this beast a true geek dream machine. I remember going to sleep with a TI-59 brochure in my hands back when I was 15 or so... (well, I was also interested in girls, so I wasn't a hopeless case!)

Of course it was an unattainable dream; a price of several hundred dollars just for the calculator itself was too much even for most American kids of my age. However, a few years later, I did in fact come in close contact with this machine, when I was writing flight simulation software for the Hungarian air traffic management authority.

As it turns out, I still have a few of those old magnetic cards in my possession. Having recently obtained a TI-59 that works really well, I was amazed to find out that the cards are actually readable after almost 20 years. It took a few tries but I was able to load, and print, several of my old programs, including the one calculating take-off distances for passenger jets under various load, runway, and engine conditions. It was amazing to see those old programs come to life, and follow the take-off of a TU-154 again as rows of numbers representing distance, speed, and altitude began to appear in printout.

Except for a richer instruction set and some keycode merging (not nearly as extensive though as the merging on HP calculators) the TI-59 has a very similar programming model to that of the SR-52. Of course those extra features made a world of a difference; for instance, the TI-59 was the first pocket calculator that knew about letters, not just numbers. Although its display used traditional 7-segment digits, the TI-59 was capable of printing arbitrary text on the PC-100 printer.

Apparently, the TI-59's card reader suffers from the same disease as Hewlett-Packard's card readers in their early calculators: the rubber of its pinch wheel disintegrates over time, turning into a yucky, gummy deposit. Because there's more friction along the card path than in HP calculators, it appears this calculator is more sensitive to the exact geometry of the wheel. So although I have made several attempts, I have yet to claim that I have repaired a TI-59's card reader to a degree that I'd call satisfactory. Fortunately, several of my TI-59s still have their wheels intact.

The TI-59 had two smaller cousins. The TI-58 had about half the memory and no card reader, which meant that programs were lost when the calculator was powered down. The TI-58C was a TI-58 with continuous memory.

All three calculators in this family have undocumented features. Most notable among these is the infamous HIR instruction, which allows the programmer to access a variety of hidden ("hierarchy") registers.

Solid-state modules really added to the power of these calculators. With these modules, it is actually possible to create a complex implementation of the Gamma function for the TI-59. The version shown here uses 309 program steps, so it fits on the two sides of a single magnetic card.

The program calculates the complex Gamma function for any complex argument, entered using the x-t key. For instance, to calculate the Gamma function of 1+3i, you'd type 1x-t3A. After a somewhat lengthy computation, the calculator will display the real part of the result (0.019292759); the imaginary part (.0338960105) can be retrieved using x-t again. To calculate the Gamma function of a real number such as 5, type 5x-t0A.

Note that this program requires the presence of the Master Library 1 module in the calculator's Solid State Library slot. If the module is not present, or if another module is inserted, the program will not function correctly.

Do you want to test drive a TI-59 yourself without spending an arm and a leg to buy one in questionable condition on eBay? I recently came across a wonderful TI-59 emulator on the Web: http://www.n3times.com/vertigo/ is the address. The emulator isn't 100% complete yet, but it's pretty darn close and it's pretty darn good, too!